The invention relates to a temperature control system for a temperature controlled chamber in an analytical instrument and, more particularly, to such a system which utilizes heating elements to control the temperature at a predetermined location within the chamber at a desired level.
Various types of chemical tests can be performed by automated test equipment, an example of testing of considerable interest being the assay of biological substances for human health care. Automated test equipment allows large numbers of test samples to be processed rapidly. Such equipment is employed in health care institutions including hospitals and laboratories. Biological fluids, such as whole blood, plasma or serum are tested to find evidence of disease, to monitor therapeutic drug levels, etc.
In the automated test instrument a sample of the test fluid is typically provided in a sample cup and all of the process steps including pipetting of the sample onto an assay test element, incubation and readout of the signal obtained are carried out automatically. The test instrument typically includes a series of work stations each of which performs a specific step in the test procedure. The assay element or cartridge is typically transported from one work station to the next by means of a conveyor such as a carousel to enable the test steps to be accomplished sequentially. The conveyor usually carries a plurality of the assay cartridges, each secured to a specific location on the upper surface of the conveyor. In the usual arrangement, the assay cartridges are spaced apart from each other in berths which are located along the periphery of the conveyor to facilitate automatic insertion and extraction.
In certain types of instruments such as those which are designed to carry out assays based on immunometric interactions between analytes or metabolites and their binding partners, the conveyor carrying the assay elements is arranged within a temperature controlled chamber since it is necessary that the assay be carried out at a a very precisely controlled temperature, for example at 37.degree..+-.0.5.degree. C. The assay elements are maintained in the temperature controlled chamber for a period of time sufficient to bring the assay element to the desired temperature prior to beginning the assay procedure and are maintained at that temperature for the duration of the process.
Various systems for controlling the temperature in such temperature controlled chambers, or incubators, have been disclosed. However, as advances are made in the design of the instruments and, more particularly, in the design and construction of the temperature controlled chambers the known temperature control systems are not entirely satisfactory. For example, consider a temperature controlled chamber which includes a slotted opening in a top wall thereof to permit a pipette to enter the chamber and dispense fluid onto an assay element being carried on a conveyor and which also includes a port in a sidewall to permit the assay elements to be inserted and removed. It is desirable, moreover, to facilitate the manufacture of the chamber and to reduce the cost of the chamber by constructing at least a portion from a moldable polymeric material.
A problem can arise in a temperature controlled chamber of this type which is made at least partly of a polymeric material in the ability to attain the required precision in keeping the temperature at the desired level. This lack of adequate control can be attributed to the poor thermal conductivity of some polymeric materials together with the frequent introduction and removal of assay elements via the port in the sidewall. By way of example, in such instruments new assay elements which are at a temperature less than that of the chamber may be introduced into the chamber at a rate of one assay element every ten seconds over a relatively short period of time. Further, in the case of a chamber constructed at least partly from a polymeric material and which has a single heating element located on the top wall, there has been observed a temperature profile in which the temperature in the vicinity of the bottom wall below the conveyor is several degrees cooler than the temperature in the vicinity of the top wall above the conveyor. In this situation stabilization of the temperature within the chamber could be effected by reducing the rate of entry of new assay elements significantly, for example, one assay element every few minutes. To do so, of course, would reduce the throughput rate of the instrument.
Accordingly, it is an object of this invention to provide a new and improved temperature control system for use in automated analytical instruments which does not require any reduction in the maximum throughput rate which the instrument can otherwise attain.